docs: def rgba_floats_tuple(self, x):
          """
          Provides the color corresponding to value `x` in the
          form of a tuple (R,G,B,A) with float values between 0. and 1.
  
          """
          if x <= self.index[0]:
              return self.colors[0]
          if x >= self.index[-1]:
              return self.colors[-1]
  
          i = len([u for u in self.index if u < x])  # 0 < i < n.
          return tuple(self.colors[i-1])